Control method for shortening start time of electric vehicle

ABSTRACT

A control method for shortening a start time of an electric vehicle quickly removes electricity remaining in a system without adding a separate component. The control method includes comparing a DC-link voltage in an inverter for driving a driving motor with a first reference value in a state in which the connection between a main battery and a vehicle system is released; checking a remaining voltage in the vehicle system and comparing the checked remaining voltage with a second reference value, when the DC-link voltage in the inverter is no less than the first reference value; removing the remaining voltage by operating an electric load in the vehicle so as to consume remaining electricity in the vehicle system, when the remaining voltage is no less than the second reference value; and connecting the main battery to the vehicle system by turning on a pre-charge relay and a main relay.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims under 35 U.S.C. §119(a) the benefit of priorityto Korean Patent Application No. 10-2012-0155825 filed Dec. 28, 2012,the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a control method for shortening astart time of an electric vehicle. More particularly, the presentdisclosure relates to a control method which can shorten a start time ofan electric vehicle by quickly removing electricity remaining in asystem without adding a separate component.

BACKGROUND

In recent years, green vehicles that can substitute for existinginternal-combustion engine vehicles are actively developed due to a highoil price, regulations of carbon dioxide emissions, and the like. Anelectric vehicle traveling by driving an electric motor and a hybridvehicle using an internal-combustion engine and an electric motor as adriving source have been or will be commercialized according tomanufacturers.

An in-wheel motor vehicle, which has an electric motor (driving motor)mounted to each wheel using power of batteries as a power source, isbeing developed among electric vehicles. The in-wheel motor vehicle is avehicle in which power is transmitted directly to each wheel by theelectric motor disposed inside a wheel rim of the wheel.

Thus, in a case where the in-wheel motor is applied to an electricvehicle, a power transmission apparatus such as a transmission ordifferential gear can be omitted, so that it is possible to decrease theweight of the vehicle and to reduce energy loss caused by a powertransmission process.

Recently, an electric bus having an in-wheel motor technique appliedthereto (referred to as an ‘in-wheel electric bus’ hereinafter) has beendeveloped. The in-wheel electric bus uses a high voltage (e.g., 486 to784V) as compared with an ordinary electric vehicle.

Accordingly, a relay in a battery system is not turned off due to itsfusion frequently in a hybrid electric vehicle (HEV), a plug-in hybridvehicle (PHEV), an electric vehicle (EV), etc., using a high voltage,which is undesirable.

Accordingly, the high voltage in the battery system is not released, ora fire or the like occurs due to heat generated in a resistance load inthe fusion of the relay.

Thus, when a high-voltage battery is re-connected to a load such as eachin-wheel motor (i.e., an inverter in a motor controller) in a vehicledriving system (e.g., in a restart after idle stop), whether the relayis turned off is checked by verifying a remaining current and itscharging state in the system, particularly before each relay of a powerrelay assembly (PRA) is turned on. Here, the PRA performs switching sothat the power of the battery is selectively supplied to an electricload in a vehicle.

Typically, whether a relay is fused or not is verified by checking aDC-link voltage in an inverter for in-wheel motor as shown in FIG. 1before a high-voltage battery (main battery) is connected to an inverterof each in-wheel motor (driving motor) (S2). In a case where it isverified that the DC-link voltage in the inverter is less than areference voltage in the checking process, a pre-charge relay and a mainrelay (high-voltage (−)/(+) relay) are sequentially turned on (S3 andS5).

However, it takes a long time to check whether the relay is turned offby verifying the discharging state of remaining current until theremaining current in the system is discharged, i.e., until the DC-linkvoltage in the inverter is less than the reference value.

Accordingly, it takes a long time to check the status of the relaywhenever the battery is connected to the in-wheel motor, since thein-wheel electric bus starts after the idle stop. This lengthens thestart time of the in-wheel electric bus, which is undesirable.

FIG. 2 is a graph showing a state in which remaining current drops in aconventional system. Here, the vertical axis represents a remainingvoltage (V) in the system, and the horizontal axis represents time(sec).

As shown in FIG. 2, it takes a long time until the remaining voltagegradually drops and then becomes less than the reference value. Hence,there is a problem in that inspection waiting time and control time arelengthened when the in-wheel electric bus starts.

A method of setting the reference value (V), at which the relay isre-joined, to be high is used for the purpose of shortening a start timeof the in-wheel electric bus. In this case, although the relay issubstantially fused, an instantaneous discharge is generated by anothervariable. Hence, there may exist a state in which the DC-link voltage inthe inverter is less than the reference value (set to high as describedabove). Therefore, a need exists for performing a process ofadditionally verifying the state. Further, the number of variablesincreases, and therefore, the control becomes complicated.

Alternatively, a method of adding a discharging resistor to a singlecomponent in the system is introduced. In the method, a dischargingresistor and a cable are additionally connected to a single component inthe driving system of the in-wheel electric bus, e.g., a motor controlunit (MCU), auxiliary machinery inverter, low-voltage DC/DC converter(LDC), high-voltage junction box, etc. The method, however, increasesthe number, size or price of the single component Therefore, the methodhas a negative influence on the optimization of the system.

SUMMARY OF THE DISCLOSURE

The present disclosure provides a control method which can shorten astart time of an electric vehicle by quickly removing electricityremaining in a system without adding a separate component.

One aspect of the present disclosure provides a control method forshortening a start time of an electric vehicle, including: comparing aDC-link voltage in an inverter for driving a driving motor with a firstreference value in a state in which the connection between a mainbattery and a vehicle system is released; checking a remaining voltagein the vehicle system and comparing the checked remaining voltage with asecond reference value, when the DC-link voltage in the inverter is noless than the first reference value; removing the remaining voltage byoperating an electric load in the vehicle so as to consume remainingelectricity in the vehicle system, when the remaining voltage is no lessthan the second reference value; and connecting the main battery to thevehicle system by turning on a pre-charge relay and a main relay.

In an exemplary embodiment, the electric load in the vehicle may be anelectrical heater for indoor heating or a heating resistor for heatinghot water, which is receives operating power applied from the vehiclesystem.

In another exemplary embodiment, the heating resistor may consume theremaining electricity by operating a chopper under the condition inwhich the remaining voltage is no less than the second reference valueand the temperature of water is no more than a reference temperature.

In still another exemplary embodiment, if the DC-link voltage in theinverter is dropped below the first reference value after the electricload in the vehicle is operated, the pre-charge relay and the main relaymay be turned on.

In yet another exemplary embodiment, the remaining voltage in thevehicle system may be a voltage at an input or output terminal of amotor control unit (MCU) for controlling the driving motor in a vehicledriving system.

In still yet another exemplary embodiment, the electric vehicle may bean in-wheel motor vehicle having the driving motor mounted to eachwheel.

Other aspects and exemplary embodiments of the disclosure are discussedinfra.

In the control method for shortening a start time according to thepresent disclosure, the remaining voltage in the system can become morequickly dropped to the reference value or less, using a heater (heatingresistor that is a resistance load) previously mounted to the vehicle,only by simply changing the control logic without adding a separatecomponent. Accordingly, it is possible to remarkably shorten the timerequired until the relay is turned on and the motor is driven.

Accordingly, it is possible to shorten a restart time of the in-wheelelectric bus, to effectively prevent loss of resistance due to theremaining current and fusion of the relay, and to increase the qualityof the vehicle by improving user safety.

Further, it is possible to solve a problem in the long control time inthe conventional method and to solve several problems occurring in theconventional method, such as an increase in the number, size or price ofthe single component due to additional connection of a dischargingresistor/cable of a single component in the system.

The above and other features of the invention are discussed infra.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features of the present inventive concept will nowbe described in detail with reference to certain exemplary embodimentsthereof illustrated the accompanying drawings which are givenhereinbelow by way of illustration only, and thus are not limitative ofthe present inventive concept, and wherein:

FIG. 1 is a flowchart illustrating a restart process including a processof verifying whether a relay is fused in a related art system;

FIG. 2 is a graph illustrating a problem according to the related art;

FIG. 3 is a schematic view illustrating the configuration of a powernetwork of an in-wheel electric vehicle;

FIG. 4 is a flowchart illustrating a control process according to anembodiment of the present disclosure; and

FIG. 5 is a graph illustrating a state in which a remaining voltage isquickly dropped by the control method according to the embodiment of thepresent disclosure.

It should be understood that the appended drawings are not necessarilyto scale, presenting a somewhat simplified representation of variouspreferred features illustrative of the basic principles of the inventionconcept. The specific design features of the present inventive conceptas disclosed herein, including, for example, specific dimensions,orientations, locations, and shapes will be determined in part by theparticular intended application and use environment.

In the figures, reference numbers refer to the same or equivalent partsof the present disclosure throughout the several figures of the drawing.

DETAILED DESCRIPTION

Hereinafter reference will now be made in detail to various embodimentsof the present disclosure, examples of which are illustrated in theaccompanying drawings and described below. While the inventive conceptwill be described in conjunction with exemplary embodiments, it will beunderstood that present description is not intended to limit theinventive concept to those exemplary embodiments. On the contrary, theinventive concept is intended to cover not only the exemplaryembodiments, but also various alternatives, modifications, equivalentsand other embodiments, which may be included within the spirit and scopeof the inventive concept as defined by the appended claims.

FIG. 3 is a schematic view illustrating the configuration of a powernetwork of an in-wheel electric vehicle. FIG. 4 is a flowchartillustrating a control process according to an embodiment of the presentdisclosure.

Referring to FIG. 3, the in-wheel electric vehicle (e.g., the in-wheelelectric bus) includes an in-wheel motor (driving motor) 50 mounted toeach wheel, an inverter and motor control unit (MCU) 40 for driving eachin-wheel motor 50, a main battery (high-voltage battery) 20 thatprovides power for driving a high-voltage auxiliary machinery includingthe in-wheel motor 50 as a major power source of the vehicle, and abattery management system (BMS) 21.

The in-wheel electric vehicle further includes a vehicle control unit(VCU) 10, a power relay assembly (PRA) 22 switching so that the power ofthe main battery 20 is selectively supplied, a high-voltage junction box30 configured between the main battery 20 and a load in the vehicle, ahigh-voltage auxiliary machinery (high-voltage electric load) 60, forexample, an air-conditioner compressor and air compressor power steeringpump, an auxiliary machinery inverter 61, an auxiliary battery(low-voltage battery) 70, a low-voltage electric load 71, for example,Vehicle electronic part, high-voltage battery cooling fan, drivingsystem cooling fan, and water pump, operated by receiving power of theauxiliary battery 70, a low-voltage DC/DC converter (LDC) 72 performinga power conversion between the high-voltage side and the auxiliarybattery 70.

Here, the VCU 10 is a most significant controller that collects variouskinds of information in the vehicle, and performs a control of thevehicle through communication with the other controller such as the MCU40 or BMS 21. Basically, the controllers in the vehicle perform thecontrol of the vehicle while transmitting/receiving informationtherebetween through communication.

For example, the VCU 10 computes a torque, based on the informationcollected in the vehicle so as to control driving of the in-wheel motor(driving motor), and the MCU 40 receives the computed torque from theVCU 10 so as to control the driving of the driving motor.

One skilled in the art will appreciate that the PRA 22 is configured toinclude a pre-charge relay (not shown) and a (+)/(−) terminal main relay(not shown). The relays are controlled to be turned on/off in responseto a relay control signal output from the BMS 21.

Meanwhile, when the vehicle is restarted after the system of the vehicleis stopped, i.e., when the vehicle is restarted after key-off or in astate of battery-off (relay-off of the PRA) in which the connectionbetween the main battery and the system gets released, the VCU 10 thatis the most significant controller verifies a remaining voltage of thesystem. In a case where the remaining voltage is no less than apredetermined level, the remaining voltage becomes quickly removed,using a heater system previously mounted in the vehicle.

A heater system for indoor heating of the vehicle, i.e., a heatingresistor 80 heating and supplying water for indoor heating is mounted inthe in-wheel electric bus.

The heating resistor 80 is an electric heating device that can be usedas a source of heating in place of the existing internal-combustionengine. The heating resistor 80 receives power supplied under theoperation of a chopper 31 in the high-voltage junction box 30, andaccordingly heats and supplies hot water for heating.

In the present example, the heating resistor 80 previously mounted inthe vehicle is used as an electric load for removing remainingelectricity so as to shorten a start time. When the remainingelectricity becomes removed, the chopper 31 operates in response to acontrol signal of the VCU 10, thereby supplying power to the heatingresistor 80.

The heating resistor 80 is an electric load to receive power appliedfrom the system. Thus, when the relay of the PRA 22 is abnormally fusedor when the remaining electricity in the system including the connectioncircuit abnormally exists, the heating resistor 80 is electricallyconnected to the system by operating the chopper 31. Accordingly, theheating resistor 80 can consume the remaining electricity in the system.

In the present example, the remaining electricity in the system becomesquickly removed through the heating resistor 80 used for indoor heating,thereby quickly dropping the voltage to the reference value or less.Subsequently, the relay is turned on so that the main battery 20 isconnected to the inverter of each in-wheel motor 50, thereby shorteningthe start time.

When the heating resistor 80 is used to quickly remove the remainingelectricity, the control logic is configured so that the remainingelectricity in the system is removed by operating the chopper 31 and theheating resistor 80 only when the remaining voltage in the system is noless than a specific voltage and when the temperature of water satisfiesa temperature condition in which the heating resistor 80 can be safelyused.

Hereinafter, the control process of the present disclosure will bedescribed in detail with reference to FIG. 4.

Referring to FIG. 4, the relays are sequentially turned on by operatingthe heating resistor for verifying whether the relay in the system isfused, verifying the remaining voltage and removing the remainingelectricity, so that a restarting process of connecting the main batteryand the inverter of each in-wheel motor is performed.

First, the VCU 10 that is the most significant controller checks anerror in the entire system by receiving diagnosis results of theindividual devices and the system through communication with the othercontrollers including the BMS 21, the MCU (including the inverter) 40for each in-wheel motor 50, the controller for the chopper, thecontroller for the auxiliary machinery inverter, and the like (S11).

In a case where an error in the system occurs, a warning is issued by awarning device (S19). In a case where no error in the system occurs, theVCU 10 verifies whether the DC-link voltage in the inverter for eachin-wheel motor (driving motor) 50 exceeds a predetermined firstreference value (S12).

If the DC-link voltage in the inverter is less than the first referencevalue, the BMS 21 receiving a signal transmitted from the VCU 10 turnson the pre-charge relay of the PRA 22. Subsequently, if the DC-linkvoltage in the inverter is in a normal state of a regulated voltage orless, the VCU 10 turns on the (+)/(−) terminal main relay (S14 and S15),so that the main battery is connected to the load (i.e., the inverter ofthe MCU) through the high-voltage junction box.

If the main battery 20 is connected as described above, the VCU 10re-checks whether an error in the entire system occurs (S16). In a casewhere no error occurs, the VCU 10 applies torque to the motor so thatthe vehicle starts (S17 and S18).

If the system is not in the normal state because the DC-link voltage inthe inverter exceeds the regulated voltage after the pre-charge relay isturned on or if it is verified that an error in the entire system hasoccurred after the main relay is turned on, the warning is issued by thewarning device (S19).

In a case where the DC-link voltage in the inverter is lower than thefirst reference value under the control between the VCU 10 and the BMS,21 the vehicle starts by turning on each relay.

Meanwhile, in a case where the DC-link voltage in the inverter is noless than the first reference value, a control process for consumingremaining electricity in the system is additionally performed. In thiscase, the VCU 10 first decides whether the heating resistor can operate.

That is, in a case where the DC-link voltage in the inverter is no lessthan the first reference value in step S12, the control process forconsuming the remaining electricity in the system is performed, and theremaining voltage in the driving system is checked (S20). If theremaining voltage in the driving system is no less than a predeterminedsecond reference value, it is verified whether the temperature of waterin the heater system is no less than a reference temperature (S21 andS22).

Here, the remaining voltage in the driving system may be a voltage at aninput or output terminal of the MCU controlling the driving of thein-wheel motor.

If the remaining voltage in the driving system is no less than thesecond reference value, and the temperature of water in the heatersystem is no less than the reference temperature, the VCU 10 transmits acommand to the chopper in the high-voltage junction box 30 so as tooperate the heating resistor (S23). Accordingly, the remainingelectricity in the system can be consumed by the heating resistor.

The heating resistor is operated as described above, so that theremaining electricity can be quickly removed. Subsequently, theoperation of the heating resistor stops in the state in which theremaining electricity is removed, and steps S12 to S17 are identicallyperformed, thereby starting the vehicle.

According to the control method of the present disclosure, the remainingvoltage in the system can become more quickly dropped to the referencevalue or less, using existing components mounted to the vehicle, only bysimply changing the control logic without adding a separate component.Accordingly, it is possible to remarkably shorten the time requireduntil the relay is turned on and the motor is driven.

FIG. 5 is a graph illustrating a state in which the remaining voltage isquickly dropped by operating the heating resistor in the control method.

Referring to FIG. 5, the remaining electricity in the system is quicklyconsumed by operating the heating resistor, so that the remainingvoltage in the system (the voltage of the input terminal of the MCU) canbe quickly dropped to the reference value (first reference value) orless within a few seconds (sec).

The inventive concept has been described in detail with reference toexemplary embodiments thereof. However, it will be appreciated by thoseskilled in the art that changes may be made in these embodiments withoutdeparting from the principles and spirit of the inventive concept, thescope of which is defined in the appended claims and their equivalents.

What is claimed is:
 1. A control method for shortening a start time ofan in-wheel motor vehicle comprising: comparing, by a vehicle controlunit (VCU), a DC-link voltage in an inverter for driving a driving motorwith a first reference value in a state in which the connection betweena main battery and a vehicle system is released; checking, by the VCU, aremaining voltage in a vehicle driving system and comparing the checkedremaining voltage with a second reference value, when the DC-linkvoltage in the inverter is no less than the first reference value;removing the remaining voltage by operating an electric load in thevehicle to consume remaining electricity in the vehicle system, when theremaining voltage is no less than the second reference value; andconnecting the main battery to the vehicle system by turning on apre-charge relay and a main relay, wherein the remaining voltage in thevehicle driving system is a voltage at an input or output terminal of amotor control unit (MCU) for controlling the driving motor in thevehicle driving system.
 2. The control method of claim 1, wherein theelectric load in the vehicle is an electrical heater for indoor heating.3. The control method of claim 1, wherein the electric load in thevehicle is a heating resistor for heating hot water, which receivesoperating power applied from the vehicle system.
 4. The control methodof claim 3, wherein the heating resistor consumes the remainingelectricity by operating a chopper under the condition that theremaining voltage is no less than the second reference value and thetemperature of water is no more than a reference temperature.
 5. Thecontrol method of claim 1, wherein, if the DC-link voltage in theinverter is dropped below the first reference value after the electricload in the vehicle is operated, the pre-charge relay and the main relayare turned on.